Resistance unit



Patented Nov.' 17, 1931 UNITED STATES PATENT OFFICE YORK NEW YORK, ABSIGNOB TO BELL TELEKOM. A. CORPORATION 0l' NIWV RESISTANCE UNIT Application aled November 88, 1927. Serial No. 885,773.

This invention relates to resistance units and to a method of making the same, andmore particularly to the type used in. lealrs and similar current ths and its ob]ect is to provide a com act orm of device in which a comparatively ong conducting path is obtained in a small ace.

In accordance with the general features of this invention a rod of suitable insulating material is provided with a tortuous or helical path suitably coated with conducting material. Preferably the conducting path is provided by threading the insulating material, coating the threaded surface with suitable conductin material and turning oi the tops or peaks o the threads to expose or bare the surface of the insulating material. Helical springs wound to substantially the same pitch as the threads of the rod engage the bottom of conducting portions of the threads and suitable contacting devices. l

As is common with resistance units of this general type the resistance element or coated rod with its helical springs may be enclosed in a suitable tube of insulating material with terminal caps or contacting devices on each end thereof and 4electrical connection made between the terminal caps and the helical sprin This invention is also applicable to forming the resistance element by interiorl threadin a tube of insulating* materia, coating ille threaded portion with conduc ing material and removing the conducting material from the peaks or tops of the thread. With the resistance element constructed in this manner the helical springs would be turned into the threaded ortion of the base to contact with the con ucting material and the terminal caps would be ap- -plied to the ends of the tubular base member.

In either case a resistance unit is provided wherein a comparatively long tortuous path of conducting material is obtained in a small space and adjustment of the resistance value of the unit may be made to fairly 'close limits by turning the helical spring members into or outof the threaded portion 0f the base member.

To more clearly explain and illustrate this invention reference will now be made to the accompanying drawings in which Fig. 1 is a view in cross section of the first described type wherein an exteriorly threaded insulat ing base member coated with conductin material in the threaded portions is use and is enclosed in a suitable tube of insulating material, and Fig. 2 is a similar view in cross section of the second described ty wherein an interiorly threaded tube of insu ating material with conducting material in the threaded portion is used. In the latter embodiment the terminal caps are fitted to the insulating base member and no outer insulating tube or enclosing member is required.

-Referring now in detail to Fig. 1, 1 is a base member of insulating material such as unglazed porcelain or any other material having the required insulating properties and havin acontinuous thread running from end to en the thread being cut or moulded into the base member whichever is found preferable, 2 is a coating of aphite or like conductin material appli to the threaded portion o the insulating base member 1. This conducting material may be applied to the insulating base member in various ways, for instance, by making a aste of the conducting material and sprea in the paste onto the threaded portion of the ase, y dipping the base into a solution containing the conducting material or by spraying the base with the solution. The method o applying the conducting material to the base member, however, is not of importance in connection with this invention. 3 represents the thread tops bared of the conductin material to form an unbroken helical path o insulating material from end to end of the threaded base member. This path may be formed by turnin or grinding oi the thread to s by rubbing t e conducting material oil this portion of the threads or by any other manner found practicable. 4 and 5 are helical spring members composed preferabl of wire wound in a helix of the same pito as the threaded portion of the base member. These spring members 4 and 5 are turned into the threads of the base member so that a plurality1 of turns of the helical spring will lie within the valley portions of the thread and make good electrical contact with the conducting materialtherein. Each spring member 4 and 5 has a straight portion 6 terminating in another straight portion 7 -extendin at right angles to the straight portion 6. and 8 are endor terminal caps of good conducting material illustrated as of a neral frustoconical shape with a central re 9 of a slightly larger diameter than the straight Egrtion 6 of the springs 4 or 5. A central ss portion 10 and a surroundin annular portion 11 with a se arating annu ar slot or groove 12 are provi ed to receive the end of a tubular casing 13.

A suitable cement or glue ma be employed in the groove 12 and along tlie inner wall surface of the annular port-ion 11 and the outer wall of the boss portion 10 to secure the terminal cap 8 to the end of the tubular casing 13.

In forming the helical spring members 4 and 5 one at least of these members is vided with an extended portion of the straight ortion 7 as illustrated at 14 by dotted lines. g'his extension iece is left on the spring member until a ter the resistance unit has been assembled and provides means by which the helical spring ma be turned further into or out of the threa ed portion of the base member while the resistance unit is under test and by this turning movement adjustment may be readil made of the resistance value of the unit tov airly close limits. After adjustment has been made of the helical s rin members by turning the helical portion urther into or out of the threaded portion of the base member solder may be applied as shown at 15 to the flat top portion of the end cap and the protruding portion 7 of the helical spring member so that some of thesolder will flow part way down the central bore 9 of the end cap and secure the straight portion 6 of the helical spring to the end cap. The end 14 of the helical spring may be severed from the straight portion 7 after the spring has been secured to the end cap.

In Fig. 2 most of the parts correspond to those shown in Fig. 1 and need no further description and explanation. The difference, however, is in the insulating base member 1, which as here shown is an interiorly threaded tubular member of insulating material with countersunk portions 16 and 17 at the ends and the internal thread extending unbroken from one countersunk end portion to the other. The countersunk end portion 17 is shown as being of greater depth than the countersunk end portion 16. This, however, is not necessary as both could be made of the same depth providing room was allowed for adjustment of the helical spring members 4 and 5 or at least one of them by aeaaeee turning further into or out of the threaded base member.

lIt will be apparent that numerous changes and modifications may be made in the structure disclosed and method of producing without departin from the spirit of the invention defined 1n the following claims.

what is claimed is:

1. A resistance unit comprising a threaded base member of insulating material, a coating of conducting material on the thread, the thread top bared of the conducting material to create a long helical path of conducting material, and caps for the unit, helical sprino members connecting the conducting materiali on the thread and the end caps, one at least of said helical s ring members having an angularly extendlng end portion for turning the helical spring within the threaded base to adjust the resistance unit to a predetermined value after said unit has been assembled.

2. A resistance unit comprising a threaded insulating base member coated with conducting material with the thread top bared on the conducting material to form a helical path of conducting material extending from end to end of the base member, end caps of conducting material and helical spring members engaging the conductingmaterial and the end caps, said end caps eing longitudinally bored, straight portions on said helical s rin members extendin longitudinally o sai base member, and t rough the end caps, and terminating in angularly disposed portions to serve as means for adjusting the resistance unit to a predetermined value after said unit has been assembled.

In witness whereof,'I hereunto subscribe my name this 22d day of November, A. D.

WINTHROP J. MEANS.

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